1. Field of the Invention
The present invention relates to a magnetic head for vertical recording involving an optical recording assist, a magnetic disk unit which carries the magnetic head for vertical recording, and information devices and products using the magnetic disk unit.
2. Description of the Background
Along with an increase in the capacity of a hard disk used in computer devices, the information recording density in a single recording surface is also increasing. In a magnetic disk unit, data is read from and written to a recording medium through a magnetic head. In order to increase the recording capacity per unit area of the magnetic disk, the surface recording density must be improved. However, as the recording density increases, the recording area (or “bit size”) occupied by one bit on the recording medium decreases.
As the bit size decreases, the energy of one-bit of information approaches a thermal energy at room temperature, and the magnetically recorded information may become inverted or disappear entirely due to thermal fluctuations. This problem is referred to as thermal decay of magnetization.
In an intra-surface recording method that has been commonly adopted, bits of magnetic information are recorded so that the direction of magnetization faces an intra-surface direction of a medium. According to this method, however, recorded information is apt to be lost by thermal decay of magnetization. To address this problem, a vertical recording method wherein magnetization signal is recorded in a direction perpendicular to a medium is gaining attention. In this vertical recording method, magnetic information is recorded based on the principle that a single pole (either N or S pole of a magnet) is approximated to a recording medium. This method is advantageous in that it is easier to prevent an unintended change of the recorded information because interaction with an adjacent inverted magnetization bit can be reduced to a minimum.
The principle of this vertical recording method is shown in FIGS. 2 and 3. FIG. 2 shows the construction of a magnetic head called a “single pole type” vertical recording head, and FIG. 3 is a sectional view thereof. This head is also called a thin film magnetic head because it is fabricated in accordance with a thin film forming technique using lithography. In an actual hard disk unit or the like, this head portion is built into a part of a 1 to 3 mm square chip called a slider 4, which has a pad structure for floating attachment thereto. Therefore, this head portion is further called a slider type thin film magnetic head.
In a main portion of the head are disposed a main pole 1 and an auxiliary pole 2. The larger pole in the shape of a rectangular parallelepiped is the auxiliary pole 2 which is for feeding back a magnetic flux. The smaller pole, having a tapered end, is the main pole 1 which has a coil 3 formed therearound. A bottom shield 8 is disposed on the opposite side of the auxiliary pole 2.
Further, a magneto-resistive element 9 (MR element, GMR element, TMR element) is disposed in a gap between the bottom shield 8 and the auxiliary pole 2 to provide a reproducing head. The head of this structure is also called a shared pole thin film magnetic head because a head portion for recording and a head portion for reproduction are structurally separated from each other. The term “magnetic head” may generally be used to refer to a combination of both the recording head and the reproducing head.
By tapering an end of the main pole, a magnetic field is concentrated to generate a recording magnetic field. On the other hand, the auxiliary pole 2 functions to pick up a magnetic flux generated by the main pole and return it again to both coil 3 and main pole 1. The auxiliary pole 2 is preferably the larger pole and is in the shape of a pillar. The main pole 1 serves as a single pole corresponding to N or S of a magnet to effect recording. The head in question, therefore, is also called a single pole head or a single pole type vertical recording head. A magnetic metal, such as permalloy may be used as the material for the main pole 1 and the auxiliary pole 2.
The magnetic field generated from the main pole 1 is recorded on a medium 5 which comprises a disk and a recording film 6 formed thereon. A thin film of a hard magnetic metal such as TeFeCo may be used as the recording film 6. This recording film serves as a magnetic recording layer. This magnetic recording layer 6 is deposited on a soft-magnetic thin film 7 such as a thin film of permalloy to afford a magnetic recording medium for vertical recording. Together, this medium 5 is simply called a magnetic medium or a recording medium. This medium 5 is disposed near the head and is rotated in the direction of arrow 15. In the disk medium 5 the thus-recorded magnetic information is formed as a magnetic pattern corresponding to S and N of a magnet at the instant of separation from a trailing-side edge of the main pole 1, as shown in FIG. 20.
In the vertical recording method, by using such a magnetic head—medium combination, the recording magnetic field faces a direction substantially perpendicular to the recording film. In the information recorded by a vertical magnetic field, the N and S poles of adjacent bits are alternated or flipped. Thus, it is difficult to form a “loop” within the film surface, so that stability is maintained easily even against a slight rotation of the recording magnetization based on heat. This is in contrast to the intra-surface recording method in which such loops occur easily. Thus, the vertical recording method is more resistive to a thermal decay of magnetization than the intra-surface recording method.
In Japanese Patent Application JP-A-195002/2000 there is proposed a method wherein the vertical recording method and an optical assist or light assist magnetic recording method are combined together. The “light assist” means the irradiation of light to heat a medium. This combined method proposes applying the light assist method used in the conventional intra-surface recording method to the head used in the vertical recording method.
Further, in Optical Data Storage Topical Meeting 2001 (Santa Fe, N. Mex., April 2001), page 130, there is described a method wherein light assist is effected by introducing light from an opposite side of a medium from the magnetic head. According to this method, a transparent glass substrate is used as the medium substrate, and light is transmitted trough the glass substrate from an opposite side of the substrate and is condensed and radiated directly to a position just under a magnetic pole.
However, in the above apparatus of JP-A-195002/2000, the light assist method adopted therein is optimized on a hard disk in the conventional intra-surface recording method which has been slightly altered to record information vertically. There has been the problem that if this light assist method is applied to a conventional vertical recording, a satisfactory light assist effect cannot be exhibited. More particularly, in JP-A-195002/2000 there is adopted a structure wherein light is introduced to a gap between a main pole and an auxiliary pole with use of a waveguide to heat between both poles. In the intra-surface recording method, a magnetization pattern is formed only at a middle point between the two poles, and it is therefore intended to perform light assist at that point. However, in the vertical recording method using a head such as that shown in FIG. 3, a magnetic pattern is formed at an edge on the side opposite to the auxiliary pole 2 with respect to the main pole 1, as shown in FIG. 20. Therefore, such pole-to-pole heating as in the intra-surface recording method is inappropriate.
Further, according to the structure adopted in this intra-surface/vertical recording method, light is projected to a narrower gap than the wavelength of light through the use of an elongated waveguide, thus giving rise to the problem that the waveguide efficiency is poor and that a practical quantity of light does not reach a portion of the disk to be irradiated. More specifically, the width of-the waveguide is smaller than the half wavelength of light, and the length thereof is as large as several microns, so that the quantity of propagated light decreases to substantially one ten-thousandth or less due to a waveguide cut-off phenomenon. In such a low efficiency waveguide structure, it is necessary to use a large-sized laser (such as of several W class) as a light source, and thus, the structure in question is not practical as a small-sized (private use) information terminal.
According to the light assist method described in Optical Data Storage Topical Meeting 2001 (Santa Fe, N. Mex., April 2001), page 130, wherein light is introduced from an opposite side of a medium, it is necessary, when assembling an apparatus, that a magnetic head 12 and an optical head 13 be disposed respectively on both sides of a medium 5 and that motions of the two heads be allowed to match and follow each other without any mechanical error, as shown in FIG. 5. In FIG. 5, reference numeral 20 denotes an optical fiber and numeral 22 denotes a rotary actuator. This apparatus construction is complicated both optically and mechanically, and an actual construction thereof as a hard disk unit results in increased costs.